Computer-aided microscopes have previously been used above all in research activities, but are now being increasingly used in commercial applications. In this connection, it has become interesting to reduce the costs of such microscopes.
FIG. 1 shows schematically an example of how a computer-aided microscope can be composed. The microscope comprises a movable microscope stage 10, on which the object 12 to be microscoped is placed, a drive mechanism 14 for moving the microscope stage, an illumination device 16 for illuminating the object, an objective 18 and an image sensor 20, which records the image of the object generated by the objective. The microscope stage 10 with its drive mechanism 14, the illumination device 16, the objective 18 and the image sensor 20 are all mounted on a microscope stand (not shown). The microscope is also provided with a controlling and analysing computer 22 with, for instance, program modules 24, 26 for analysing images and for controlling the drive mechanism. The microscope may also have other hardware and software components which are normally to be found on a microscope, but these components will not be discussed or shown in the Figure since they are now of no interest to the present invention.
A hardware component which is relatively expensive is the microscope stage with its drive mechanism. The reason for this is that high requirements are placed on the combination of microscope stage and drive mechanism.
First, it should be possible for the drive mechanism to position the object with repeatability. By this is meant that a position that has been reached and noted once should be found a second time at request, in a reliable fashion. The time from the request to the position being found again should be short. The accuracy with which the position is found again is not allowed to be too poor. The accuracy should be at least such that the partial object which is located in the searched position is at least found again in the usable part of the image field of the microscope. By usable part is meant that the current partial object, after one focusing, can be discovered also this second time.
Second, the drive mechanism should be able to move the microscope stage so accurately in two dimensions that the entire object can be scanned without parts thereof being unintentionally missed, but yet with such a small overlap between succeeding images that the scanning can be made rapidly.
If it should be possible to satisfy the above-mentioned requirements as regards the drive mechanism in a system without feedback, it is necessary to use very accurate components without play, such as stepping motors and screws of the type that is used in numerically controlled machine tools. However, such components are quite expensive.
Alternatively, position sensors 25 which detect the position of the microscope stage can be installed, and a feedback control system can be used for the positioning. This is shown schematically in FIG. 1 with dashed lines. The drawback of this is, however, that it will be necessary to install additional components which can break, increase the cost of the microscope and need space.
EP 0 731 371 discloses a system for controlling a microscope stage. A camera records an image of an object on the microscope stage. The microscope image is shown on a display. The user marks an interesting area or an interesting point in the microscope image on the display by means of a pointing device. As this takes place, a computer program enters the current coordinates from the control electronics of the microscope stage. The computer program has been calibrated with information about the image size of the camera. Thus, the computer program can calculate coordinates of the marked area or the marked point. The computer program then directs the microscope stage to these coordinates. However, this requires a repeatable drive mechanism for the microscope stage, which has up to now been provided using expensive screws and stepping motors or position control with extra position sensors.